This invention relates to high ethylene ethylene-vinyl acetate (EVA) emulsions comprising a water dispersible copolymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt. The invention also relates to ethylene-vinyl acetate emulsions containing at least 55 percent by weight of ethylene, and a process for producing said high ethylene EVA emulsions. The invention also relates to emulsions comprising a water dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt, where the polymer has a Tg of less than 25xc2x0 C.
Ethylene-vinyl acetate (EVA) polymers provide useful properties at relatively low cost in many industrial applications. Ethylene monomer is a low-cost monomer and therefore incorporation of as much ethylene as possible into an ethylene-vinyl acetate polymer allows one to take advantage of cost and performance benefits.
U.S. Pat. No. 3,644,262 discloses a process for increasing the ethylene content of an EVA emulsion. An ethylene content of 5 to 40 percent is targeted in the patent, and examples of copolymers containing 11 to 21 percent ethylene are cited.
EP 0 990 688 describes an EVA pressure sensitive adhesive containing carboxyl monomer. Said PSA has an ethylene content of greater than 45 percent, and most preferably from 45 to 55 percent.
Salt sensitive polymers are dispersible in water, but non-dispersible in salt solutions. Said polymers are useful in applications where a film is desired which will dissolve or disperse in water. Such applications include polymer products which can be disposed of in water, where the film will disperse.
U.S. Pat. No. 5,312,883 discloses a composition of a water-soluble polymer that is insoluble in 0.5% salt solutions. The composition requires 30 to 75% acrylic acid, 5 to 30 percent of a C8 to C12 alkyl (meth)acrylate, and 20 to 40 percent of a C2 to C4 alkyl (meth)acrylate. The disclosure is limited to acrylic acid copolymers and specific (meth)acrylates. Also, the disclosed process for preparing these polymers is costly and time consuming.
WO 00/38751 discloses an ion-sensitive polymer which is insoluble in a neutral salt solution containing at least 0.3 weight percent salt, and is soluble in tap water containing 15 ppm to 500 ppm of one or more multivalent ions. Said polymers are formed as solution polymers.
U.S. patent application Ser. No. 09/540,033 describes salt sensitive aqueous emulsions which are non-dispersible in aqueous solutions containing 0.5% or more of an inorganic salt which contain a copolymer of an 10 to 90 percent of an acid monomer and a second monomer.
Surprisingly, it has been found that EVA emulsion polymers containing a high level of ethylene can be produced without a carboxyl-containing monomer. Said polymers, using other functional comonomers, produce better properties than carboxyl-containing EVAs. It has also been found that stable EVA emulsion polymers, having an ethylene content of greater than 55 percent by weight, can be obtained. Also, it has been found that emulsions can be produced which form flexible films that are dispersible in water but not in an aqueous solution containing 0.5 percent or more of an inorganic salt. The combination of these two findings yields a high ethylene content ethylene-vinyl acetate emulsion polymer capable of forming a film which is redispersible in water but non-redispersible in a 0.5 percent or greater inorganic salt solution.
The present invention is directed to an ethylene-vinyl acetate emulsion polymer comprising:
a) a copolymer of ethylene and vinyl acetate having greater than 55 percent by weight ethylene; and
b) a hydrophilic polymeric colloid stabilizer
wherein said hydrophobic colloid comprises from 1 to 100 percent by weight of an acidic ethylenically unsaturated monomer; wherein said ethylene-vinyl acetate copolymer is water-dispersible, and wherein said ethylene-vinyl acetate copolymer is non-dispersible in an aqueous solution containing 0.5 weight percent or more of an inorganic salt.
In a second embodiment, the present invention is directed to an aqueous emulsion comprising a water-dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt, wherein said water-dispersible polymer comprises from 1 to 100 percent by weight of a hydrophilic monomer and from 0 to 99 percent by weight of at least one non-hydrophilic monomer, wherein a film formed from said polymer has a Tg of less than 25xc2x0 C.
In a third embodiment, the present invention is directed to a high ethylene, ethylene-vinyl acetate emulsion polymer comprising greater than 55 percent by weight of ethylene, and to a process for producing said high ethylene content EVA polymer.
The present invention is directed to salt-sensitive emulsion polymers containing a water-dispersible polymer which is non-dispersible in aqueous solutions containing 0.5 weight percent or more of an inorganic salt. The invention is also directed to an ethylene-vinyl acetate emulsion polymer having at least 55 percent by weight of ethylene, and a process for producing said emulsion polymer. The invention is also directed to a combination of the above two concepts producing a high ethylene content EVA emulsion polymer which is water-dispersible, yet non-dispersible in an aqueous solution containing 0.5 percent or more of an inorganic salt.
Salt sensitive emulsion polymers are polymers which are formed by an emulsion polymerization process, and which form films that are dispersible in tap water, yet are non-dispersible in water containing at least 0.5 percent by weight of an inorganic monovalent, divalent, or trivalent salt, or mixtures thereof The polymer is dispersible, rather than soluble, in water. Dispersible, as used herein, means that in tap water, a film formed from the polymer breaks into small discrete pieces or particles that can be filtered out. These pieces are capable of being filtered from the water. While not being bound to a theory, it is believed that the dispersion of the polymer film is related to the fact that a film forms from an emulsion by coalescence of polymer particles, forming weak bonds between particles. In water, some bonds between the particles will break, resulting in clusters of polymer particles. This is different from a solution polymer in which polymer chains mix and entangle during film formation, and this film dissolves into individual polymer chains, which cannot be filtered. Since the polymer contains a high level of hydrophilic monomer(s), when the emulsion dries to a film, the particles are easily dispersed in water.
The emulsion polymers of the present invention consist of a polymer which is stabilized by a hydrophilic polymeric colloid. The polymer itself is not salt sensitive. The colloid may or may not be salt sensitive. However, the colloid-stabilized polymer particle is salt sensitive.
The polymer colloid contains at least one monomer, and ideally two or more monomers. At least one of the monomers is a hydrophilic monomer.
The hydrophilic monomer may be an acidic monomer containing a carboxylic acid, a dicarboxylic acid, a sulfonic acid, or a phosphonic acid group, or a mixture thereof. Examples of carboxylic acid monomers include, but are not limited to, acrylic acid, methacrylic acid, maleic acid, maleic acid half esters, maleic anhydride, itaconic acid, and crotonic acid. Preferred carboxylic acids include acrylic acid and methacrylic acid. Sulfonic acid monomers include, but are not limited to styrene sulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, vinylsulfonic acid, and the salts of these acids. Examples of monomers containing a phophonic acid group include, but are not limited to styrene phosphonic acid, sodium vinyl phosphonate, vinylphosphoric acid, and CH2=C(CH3)COO(CH2)nOPO3H, where n is from 2 to 4. A preferred phosphoric acid monomer is vinyl phosphonic acid. Other hydrophilic monomers include, but are not limited to, those containing a hydroxyl group, acrylamides and methacrylamides.
The polymer colloid may also contain at least one other monomer. Examples of monomers useful in the present invention include but are not limited to
(Meth)acrylamide, N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, N-butyl (meth)acrylamide, N-t-octyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-dibutyl (meth)acrylamide, N,N-di-t-octyl (meth)acrylamide, 2-(dimethylamino)ethyl (methacrylate), N-[3-(dimethylamino)propyl] (meth)acrylamide, N-metholyl (meth)acrylamide, N-(isobutoxymethyl)acrylamide, acrylonitrile, N-vinyl formamide, vinyl pyrrolidone, N-caprolactam, t-octyl (meth)acrylamide. Those skilled in the art can envision linear and branched versions as well as higher alkyl chains.
Vinyl formate, vinyl acetate, vinyl propionate, vinyl isobutyrate, vinyl pivalate, vinyl 2-ethylhexonate, vinyl p-t-butyl berzoate, vinyl ester of versatic acid (i.e. Veo Va 10, Veo Va 11, Veo Va 12), vinyl laurate, vinyl stearate, vinyl eichoanate, vinyl docosanate. Those skilled in the art can envision linear and branched versions as well as higher alkyl chains.
1-Hydroxymethyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 1-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 1-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate. Those skilled in the art can envision linear and branched versions as well as higher alkyl chains.
Ethylene, propylene, butylene, butadiene. Those skilled in the art can envision linear and branched versions as well as higher alkyl chains.
Methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate2-ethyl hexyl (meth)acrylate, octyl (meth)acrylate, t-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isobomyl (meth)acrylate, lauryl (meth)acrylate, steryl (meth)acrylate, cyclohexyl(meth)acrylate, 1-hydroxymethyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 1-hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 1-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate.
The hydrophilic monomer(s) is present in the polymer colloid at from 1 to 100 percent by weight. Other ethylenically unsaturated monomers may be present at from 0 to 99 percent by weight. Preferably the hydrophilic monomer is present in the polymer colloid at from 10 to 100 percent and most preferably from 30 to 99.
A graft-linker and/or crosslinker can be incorporated into the polymer colloid. Examples of graft-linkers and/or crosslinkers useful in the present invention include, but are not limited to, diallyl phthalate, diallyl amine, allyl methacrylate, ethylene glycol diacrylate, 1,6-hexane diacrylate, methylene bisacrylamide, divinyl benzene, triallyl amine, triallyl cyanurate, and trimethylolpropane triacrylate.
The polymer colloid of the invention may be used to stabilize a latex polymer. The colloid itself can be either salt sensitive or non-salt sensitive. The colloid can either be added to the polymerization process separately, or be formed in situ.
Examples of colloids that are salt sensitive include, but are not limited to, poly(acrylic acid), poly(methacrylic acid), and copolymers thereof.
Examples of colloids that are not salt sensitive include, but are not limited to, the salts of poly(2-acrylamido-2-methyl-1-propanesulfonic) acid, the salts of polyphosponic acid, and polyols.
The colloid is present in the latex polymer at from 0.1 to 100 percent by weight based on polymer solids, more preferably 1 to 75 weight percent, and most preferably from 3-75 weight percent.
The latex polymers of the present invention have a Tg of below 25xc2x0 C. and preferably below 0xc2x0 C. Films formed from these polymer emulsions are flexible at room temperature.
The process for producing salt sensitive emulsions of the invention involves the formation of a colloid stabilizer, followed by an emulsion polymerization using said stabilizer by means known in the art. The stabilizer may either be formed in situ, or added separately. A useful process for producing the salt sensitive emulsions is found in U.S. patent application Ser. No. 09/540,033, incorporated herein by reference. The emulsion polymerization may be a batch, semi-batch, or continuous process.
One preferred process involves an in situ colloid process in which a polymer seed is polymerized from one or more monomers selected from unsaturated acidic monomers, alkyl(meth)acrylates and vinyl monomers which are neutralized to between 1 and 100 percent with base to form a stabilizer. Using this stabilizer, monomers are added and polymerized by means known in the art of emulsion polymers.
Another preferred process involves the use of a hydrophilic polymer colloid, as described above as a stabilizer in the synthesis of an ethylene-vinyl acetate copolymer, where the level of ethylene in the copolymer is at least 55 percent by weight of the polymer.
The salt sensitive emulsion polymer is useful in protective top coats, floor polishes, temporary printing, adhesive binders, skin creams, sun screens, temporary decorative paints, marine coatings, repulpable paper coatings, glass fiber sizing, time release/erodable coatings or particles, and personal care products such as, for example, an antiperspirant film not removed by perspiration but removed by soap and water.
The emulsion polymer may be part of a final formulation containing components known in the art in conventional amounts. The other components may include, but are not limited to, plasticizers, tackifiers, fillers, humectants, and surfactants.
The present invention also relates to ethylene-vinyl acetate emulsion copolymers containing greater than 55 percent by weight of ethylene, and a process for producing said polymers. Preferably, ethylene is present in the polymers at a level greater than 55 percent by weight, more preferably greater than 60 percent by weight, and most preferably at a level greater than 65 percent by weight.
In addition to ethylene and vinyl acetate, the polymers of the present invention may optionally include one or more other ethylenically unsaturated monomers. Preferably, the high ethylene EVA copolymer is free of carboxyl containing monomers such as acrylic and methacrylic acid. Monomers useful in the present invention may include functionalized monomers. Examples of functionalized monomers useful in the present invention include, but are not limited to nitrogen functional monomers, vinyl esters, alcohol functional monomers, and (meth)acrylates. Preferred monomers include N-methylol acrylamide, acrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, acrylamidopropyl sulfonate and salts thereof, acrylonitrile, ammonium acrylamidylpropyl sulfonate. An especially preferred functionalized monomer is N-methylol acrylamide. A functionalized monomer may be present in the polymer at a level of up to 25 percent by weight, preferably up to 20 percent by weight, and most preferrably up to 15 percent by weight, based on the polymer.
The emulsion polymer is formed using a stabilizer. The stabilizer can be either a surfactant or a colloid. The surfactant can be any surfactant known in the art. Preferably the surfactant is an anionic or non-ionic surfactant, or a mixture of said surfactants. A preferred non-ionic surfactant is a non-alkoxyphenol-based surfactant. Preferably the surfactant is an ethoxylated alcohol. Preferred anionic surfactants are sulfonate or sulfate salts, most preferably sulfosuccinic acid derivatives.
The emulsion polymer can be formed by a surfactant-free process using a polymeric colloid stabilizer. The colloid stabilizer may be formed in situ or added separately. By selecting a colloid stabilizer, as described above, the EVA polymer can be salt sensitive.
The EVA emulsion polymer is formed using the following process. A small initial charge is added to a reactor, preferably from 0 to 10 percent based on the weight of polymer. The initial charge and slow feed contain an amount of stabilizer sufficient to maintain emulsion stability, preferably from 0.5 to 10 percent by weight based on the weight of the polymer. Ethylene pressure is maintained in the reactor at a pressure above 500 psi, preferably above 1100 psi, and most preferably from 700 to 1400 psi, from before initiation until after the reaction is complete. The conversion is kept high throughout the reaction by sufficient agitation and a temperature high enough to ensure rapid conversion, yet low enough to encourage ethylene solubility. The temperature of the reaction is maintained at from 25 to 100xc2x0 C., and preferably at from 50 to 80xc2x0 C. A slow monomer feed is used, lasting from 1 to 10 hours, preferably from 2 to 6 hours and most preferably from 3 to 5 hours.
Formation of the EVA emulsion polymer is facilitated by the use of a polymerizable stabilizer such as sodium vinyl sulfonate, vinyl phosphonic acid, acrylamido-2-methyl-1-propanesulfonic acid, and their salts and derivatives. Preferably, the polymerizable stabilizer is sodium vinyl sulfonate. The polymerizable stabilizer is incorporated into the polymer at from 0 to 5 percent by weight, preferably from 0.1 to 4 percent by weight, and most preferably from 0.5 to 3 percent by weight, based on the weight of the EVA polymer.
High ethylene content EVA polymers have excellent peel and shear properties. The polymers also exhibit excellent tack without a tackifier. High ethylene EVAs are useful in repulping operations allowing paper to be recycled without requiring removal of the polymer in a separate expensive step. High ethylene EVA polymers are also useful in many industrial application such as, but not limited to, pressure sensitive adhesives, nonwoven binders, paper saturation binders, repulpable paper coatings, adhesive binders, salt-triggerable polymer systems.
The polymers of the present invention can be used to produce environmentally friendly products, such as less expensive paper recycle and flushable hygienic products.
This invention will be further clarified by use of the following examples which are not intended to restrict the scope of the invention. For examples 1-24, the copolymer was prepared in a 10 liter stainless steel medium pressure reactor. The reactor was equipped with a jacket for heating and cooling, a two-blade 45 degree pitched blade turbine and metering pumps for addition of various reaction components. Only deionized water was used for these batches.
The ethylene content was measured using a C-13 NMR technique in which the splitting of the xe2x80x94-CHOAc-carbon is integrated.